Tapping into heightened security fears after the Paris terrorist attacks, House Republicans — joined by many Democrats — rebuffed President Obama on Thursday and overwhelmingly approved legislation that would in effect halt the resettlement of refugees from Syria and Iraq to the U.S.

Faced with a White House veto, Republican leaders in Congress are threatening to include the restrictions in a must-pass spending bill to keep the federal government running past Dec. 11, raising the specter of another government shutdown.

The House bill would require leaders of the nation's security apparatus — the director of national intelligence and the heads of the Department of Homeland Security and the FBI — to certify that refugees who are admitted pose no security threat.

The White House, which has proposed admitting at least 10,000 refugees to the U.S. this fiscal year from war-torn Syria, said the House bill creates “unnecessary and impractical requirements,” noting the current screening process is rigorous and takes up to 24 months. Critics say the legislation would essentially shut down the program. Prospects for passing the measure in the Senate remain uncertain.

The House approved the measure 289 to 137, with several dozen Democrats joining Republicans, crossing the threshold needed to overcome a presidential veto. But House Minority Leader Nancy Pelosi (D-San Francisco) vowed that a veto would be sustained.

The issue has lighted up the presidential campaign trail, with Republicans divided and Democrats siding with the White House.

“Turning away orphans, applying a religious test, discriminating against Muslims ... that's just not who we are,” said Hillary Clinton, the Democratic presidential front-runner.

Republicans, who say the current vetting process cannot guarantee terrorist sympathizers won't slip into the U.S. undetected, may decide to test Obama's resolve in the weeks ahead. The political battle is taking shape as a slight majority of Americans in two new polls said they wanted to restrict Syrians coming to the U.S.

Conservative groups, including Heritage Action, opposed the legislation, saying it did not go far enough in curtailing security risks. They want to block part of the broader $500 million the State Department has requested for its refugee settlement program worldwide next year.

Cruz had suggested permitting only Christian refugees from Syria into the country, but such a condition is not part of the House bill.

Despite the robust bipartisan support in the House, the issue has split along partisan lines among the public.

Eight in 10 Republicans disapprove of admitting more Syrian refugees, while two-thirds of Democrats agree with the White House, according to an NBC News/SurveyMonkey online poll released on the eve of the vote. Independents side mostly with Republicans on the issue, according to the poll.

Senate Democrats were preparing an alternative measure to slap controls on a visa waiver program, which currently allows up to 20 million visitors a year from certain countries to enter the U.S. without biometric and in-person screening. Some experts say loopholes in the waiver program pose the bigger security problem.

“The country is uneasy and unsettled,” said House Speaker Paul D. Ryan (R-Wis.). “Our first priority is to protect the American people. We can be compassionate, but we can also be safe.”

The administration is struggling to tamp down opposition to the decades-old resettlement program that has enjoyed bipartisan support since it was launched in the aftermath of the Vietnam War.

But for many House Democrats under pressure to show they are tough on terrorists, the issue is “toxic” at home, according to one Democratic aide. A morning meeting with Homeland Security Secretary Jeh Johnson and White House Chief of Staff Denis McDonough before the vote “was not going over well,” according to the aide, granted anonymity to discuss the private session.

White House officials say the House restrictions are unneeded. Unlike the steady stream of male migrants flowing into Europe from Syria, the State Department says those admitted to the U.S. are different demographically.

Half of the Syrian refugees are children and young people, and 24% are males over the age of 21, according to the State Department's Worldwide Refugee Admissions Processing System. The vast majority of those men are coming with family members rather than alone, according to the State Department.

Of the Syrian refugees admitted to the United States in recent years, the administration said “not a single one has been arrested or deported on terrorism-related grounds.”

Also Thursday, FBI Director James B. Comey announced that while U.S. law enforcement officials were on heightened alert following the Paris attacks and pledges by Islamic State to strike New York and Washington, federal law enforcement agents had not substantiated any “credible” threats at this time.

“We began looking for connections between Paris and here” immediately after last week's attacks, he said, “and made sure we were tightly connected with our state and local partners.”

Federal law enforcement typically works about 900 “active” terrorism investigations at any given time, authorities have said, many of which end in arrests and charges for providing support to Islamic State and other terrorist groups. There are an additional four dozen cases in the U.S. being worked by the FBI's 24-hour Special Surveillance Group.

Only a few of the cases slip through, such as the attempted attack in May in Garland, Texas, against a cartoon contest belittling the prophet Muhammad. In that incident, two Phoenix men were gunned down by police before they could open fire on the convention.

“Do not let fear become disabling,” Comey said in encouraging the American public to remain vigilant. “That is what the terrorists want.”